People are generally aware of the most common causes of hallucinations, like schizophrenia and a really high fever. But lesser known are the more rare causes; here are six you probably haven't heard about.

The difference between a “plain Jane” and a “saucy Sue” can be picked up by the naked eye in just seconds because we are visually stimulated beings. The face acts as an inaudible social instrument that comes in different colors, shapes, and sizes, which is essential for facial recognition. Since most of our daily social interactions are largely done face-to-face, many of us are under the false pretense our face is who we are, so we're sure to generously layer it with cosmetics, grow out facial hair, or mark it up with tattoos or piercings to set ourselves apart from the rest. Robert Lamb from the YouTube channel, “Stuff to Blow Your Mind,” explores what our face can say about us based on the often subtle, non-vernal signals we give to others unconsciously.

"The face is like a speaker, constantly blasting the world with the course of seven primary emotions: that's happiness, sadness, fear, anger, surprise, disgust, and contempt," says Lamb in the video, “Find Out What Your Face says about You - Epic Science #16.” These facial expressions, along with the micro expressions that are there for just fractions of a second, can actually speak up to 1,000 different words, without opening our mouths. Our expressions can be very telling of the state of mind we’re in, and how we feel at the time.

Alongside facial expressions, facial features play an important role when it comes to perception from others. In a 2012 study published in the journal Proceedings of the Royal Society B, researchers found the more solitary a species of a primate, the crazier the faces tend to be, and vice versa. This suggests we don’t necessarily have to distinguish ourselves physically to socially attract people.